#include <algorithm>
#include <bits/stdc++.h>
#include <cstdlib>
#include <functional>
using namespace std;

#ifndef ONLINE_JUDGE
    #include <bits/debug.h>
#endif

#define int int64_t
#define endl "\n"

using PII = pair<int, int>;
using TII = tuple<int, int, int>;
template<class T> using V = vector<T>;
using i64 = long long;
using i128 = __int128;
using u64 = unsigned long long;

#define FOR(i, a, b) for (int i = (int)(a); i <= (int)(b); i++)
#define FOR2(i, a, b, c) for (int i = (int)(a); i <= (int)(b); i += (int)(c))
#define FORD(i, b, a) for (int i = (int)(a); i >= (int)(b); i--)
#define FORD2(i, b, a, c) for (int i = (int)(a); i <= (int)(b); i -= (int)(c))
#define ALL(a) a.begin(), a.end()
#define RALL(a) a.rbegin(), a.rend()
#define lowbit(x) ((x) & (-x))
#define RE return;
#define Yes cout << "Yes" << endl;
#define YES cout << "YES" << endl;
#define No cout << "No" << endl;
#define NO cout << "NO" << endl;
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define sz(x) (int)(x).size()

void solve() {
    int n;
    cin >> n;

    V<int> w(2 * n + 1, 0);

    FOR(i, 1, n * 2) cin >> w[i];

    int ans = 1e18;

    function<void(int, int)> dfs = [&](int u, int t) {
        if (u > n || u >= ans) {
            RE;
        }

        if (is_sorted(ALL(w))) {
            ans = min(ans, u);
            RE;
        }

        if (!t) {
            FOR2(i, 1, n * 2 - 1, 2) {
                swap(w[i], w[i + 1]);
            }
            dfs(u + 1, t ^ 1);

            FOR2(i, 1, n * 2 - 1, 2) {
                swap(w[i], w[i + 1]);
            }
        } else {
            FOR(i, 1, n) {
                swap(w[i], w[i + n]);
            }

            dfs(u + 1, t ^ 1);

            FOR(i, 1, n) {
                swap(w[i], w[i + n]);
            }
        }
    };

    dfs(0, 0);
    dfs(0, 1);

    if (ans == 1e18) ans = -1;

    cout << ans << endl;
}

signed main() {
    int Task = 1;

    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    while (Task--) {
        solve();
    }

    return 0;
}
